This invention relates to the preparation of rubbery polymers with low molecular weights by a controlled degradation reaction applied to unsaturated hydrocarbon elastomers. It covers a novel method and the novel products obtained at the various stages of their manufacture.
Many attempts have been made to simplify the processing of natural and synthetic rubbers, which resorts to masticating, mixing, and high-temperature and high-pressure moulding methods. Such operations heavily burden the cost of manufactured articles. To avoid the use of such costly equipment as masticating mills and vulcanizing presses, attempts have therefore been made to use rubbers under a fluidified form, notably as a dispersion in water, known as a latex. Until now, the direct use of latex has remained limited. The difficulties encountered when reinforcing the material, as well as the uncertain dimensions of parts, due to shrinking owing to difficult elimination of water, explain that such methods have not been used industrially, e.g. for the manufacture of tyres. It seemed therefore suitable to use, instead of a latex, a material having a fluidity, that would be ascribable not to the presence of a foreign liquid phase, but to an intrinsic property, directly resulting from its low degree of polymerization. Indeed, a large amount of research work on the preparation of such liquid elastomers is being actively carried out all over the world since many years. The method used is mostly radical or anionic polymerization of monomers such as butadiene, styrene etc. The literature contains many patents and papers on the subject.
However, another way leads to oligomers with low molecular weights: this makes use of controlled depolymerization of hydrocarbon macromolecules. Historically speaking, this was the method which lay behind the coming out on the market in 1923 of the first liquid rubbers (D.P.R., manufactured by Hardman). Since then, various attempts have been made using thermal or mechanical energy or the action of some chemical peptizers (Farbenfabriken Bayer, B.P. 693 331, 24 June 1953), but they have not led to oligomers which can be used in casting, transfer or injection methods. Recently, however, a low molecular weight polybutadiene with carboxyl end groups has been obtained by ozonolysis of a stereo-regular poly-1,4-cis-butadiene (D.P. Stephens, R.C. McIntosh and O. Taylor J. Polymer Sci. A-1, Vol. 6 (1968), p. 1037).